What is altitude sickness and what can you do about it?

It is often thought that it is something that you only encounter at high altitudes such as in Himalayas: altitude sickness. But you’re at risk as ‘low’ as 2,500 meters. More and more places in the world are becoming accessible to tourists, including beautiful mountain areas where you have a real chance of suffering from altitude sickness. But what exactly is altitude sickness? And more importantly: how do you recognize it and what can you do about it?

Oxygen and oxygen deficiency

Altitude sickness is a result of oxygen deprivation in your body. The higher you get, the fewer oxygen molecules there are in the air. This is due to the weight of air: at sea level, the air is compressed by all the air above it that presses it down. The higher you get, the less air you have above you. So there is less air on you. As a result, the air pressure is lower and there are fewer oxygen molecules in the air. Your body starts to suffer because it can get less oxygen from the air every time you breathe. Your heart will beat faster and your breathing accelerates. Not surprising, because your body still has the same need for oxygen.


This video explains it all:

Risk of altitude sickness

Many people think that you can only suffer from altitude sickness at “extreme” altitude, such as in the Himalayas. This is a big, and also a dangerous mistake. Altitude sickness also occurs regularly in the Alps at a relatively low altitude. This does not apply to trips where you walk up and descent again within 8 hours. You can suffer from some light headaches and dizziness, but the time to develop serious symptoms is simply too short. Below is a general overview of the average chance of altitude sickness at different heights to give you a bit of an idea:


  • 2.500 to 3.500 meters: 25% chance of mild form of altitude sickness
  • 3.500 to 5.500 meters: 65% chance of more serious and sometimes even fatal forms of altitude sickness
  • 5.500 to 8.850 meters: nearly 100% chance of mild to very severe forms of altitude sickness


Sounds intense, right? But it’s important to know that when you’re hiking between 3.500 and 5.500 meters, you could get altitude sickness and that it can even be fatal. Especially when you think about the fact that mountainous areas at 3.500 meters are still fairly accessible for most people. However, you do have to take into account that there’s a 2000 meters difference in this scale. And the risk is considerably higher when you’re in an area at 5.500 meters. But, underestimating the risk, overestimating yourself or simply not recognizing the signals and not knowing what to do can make the situation a lot worse.


Other risk factors for altitude sickness are: 


  • Rapidly rising from sea level to above 2,500 meters, or rising above that altitude faster than 300 meters per day without rest days. You can climb more than 300 meters in one day but then descent again to a maximum of 300 meters above your starting point to stay overnight.
  • Being overweight.
  • Predisposition. People who have had altitude sickness while they’ve stuck to the advice, are at greater risk of getting sick again next time.
  • Fitness. It may sound weird, but people who are really fit are at greater risk of getting sick. While you should definitely be fit when you go up in the mountains, it turns out that fit people tend to want to climb too fast because they feel good. Altitude sickness is something you don’t always feel immediately, it takes a while before you get bothered by it. As a result, they run a greater risk of altitude sickness.
  • Diseases that you might have before an ascent. In particular, some heart and lung diseases can have a big effect.

Being fit is a requirement, but also a dangerous pitfall

Preventing altitude sickness

Despite the list shown above, you have a big say in whether or not you’ll get sick or (if you go higher) how severe it will be. If you have traveled around at higher altitudes before, you will be able to recognize the symptoms yourself. Are you going up to serious hights for the first time? Make sure you come prepared! Read about the symptoms of altitude sickness and check out the tips below. By applying these tips, altitude sickness under 5,000 meters can be prevented for most people. At the very least it will be a lot less severe and you’ll avoid serious problems. So you can still enjoy your trip in the mountains.


  • Make sure you recognize the symptoms belonging to altitude sickness.
  • Don’t ascent to fast from sea level to sleeping heights above 2,500 meters.
  • Do you want to climb further than 2,500 meters? Make sure you sleep one or two nights at this altitude before continuing. 
  • When you’re above 2,500 meters, don’t sleep more than 300 meters higher than the previous night. 
  • Don’t continue ascending when you’re experiencing symptoms that don’t disappear with some simple painkillers. Wait until you’re completely fine again.
  • If your complaints get worse despite having a rest day or walking at the same height, you should always descent.
  • Make sure you have a rest day for every 1,000 meters you’ve climbed. Or at least stay at the same altitude
  • Prevent dehydration by drinking enough. Assume you’ll need an extra liter of water for every 1,000 meters you go higher.
  • Don’t smoke, your lungs are suffering enough.
  • Do you already suffer from heart or lung diseases or any other type of illness? Make sure you talk to your doctor about your travel plans.



Hoogteziekte - Pisang

Pisang, a village in the Himalaya mountains in Nepal

What are the symptoms of acute altitude sickness?

To recognize altitude sickness, you need to know what are the signals and symptoms are that indicate this. Because your body has to adapt to the new circumstances, you should not be surprised if the symptoms start to appear after you’ve been at your destination for a few hours. Regular altitude sickness is also called acute altitude sickness. These are the signals that you might suffer from acute altitude sickness:


  • A headache
    • This isn’t a severe sign of altitude sickness. If the headache disappears when you take simple painkillers, there’s no reason to take action. But make sure you’re paying attention to other symptoms. Even if painkillers don’t help this is not necessarily disturbing, but mainly ‘just’ annoying. Don’t ascent any further, but wait till the pain is completely gone (usually one or two days). Definitely DON’T continue climbing with a headache that doesn’t go away, despite taking painkillers. 
  • Problems sleeping
    • Having trouble sleeping is also a common complaint. Many people have weird or lively dreams when high up in the mountains. Also, a less constant breathing is a recognizable complaint and sometimes you wake up feeling stuffy. This is annoying, but not serious.
  • Shortness of breath
    • Because of the fact that there are fewer oxygen molecules in the air, breathing takes more effort, especially when you also make an effort (like climbing).
  • Dizziness
    • Dizziness is something that occurs less often, but it is a signal for possible acute altitude sickness. This is due to oxygen deprivation in your brain but is not harmful either. If you go to really great heights, above 6,000 m, it can become dangerous if you can not properly assess situations due to the lack of oxygen. You will not recognize this yourself, which makes it very important to keep a close eye on each other as a group.
  • Fluid retention in arms, legs or face
    • Despite being low in fluids, you could suffer from water retention. Your body simply doesn’t know what to do with this fluid. 
  • Excessive fatigue
    • Being really tired isn’t a concerning symptom on its own. But in some cases, it can be a signal of (incipient) pulmonary edema, fluid behind your lungs. This is a life-threatening situation.
  • Little to no appetite
    • Although you may not be hungry, it is really important to keep eating well and often. No matter how hard this may be for you. Your body makes a physical effort, so you need that energy.
  • Nausea or vomiting
    • This may be because your body is trying to send more blood and oxygen to your vital organs at the expense of your stomach. If you have to vomit as a result, make sure you’re drinking plenty of water to prevent dehydration.
  • Having to pee less often
    • It’s important to drink enough. Make sure you drink an extra liter for every 1000 meters you ascent.  


Many of these symptoms can also be attributed to other reasons. Everyone suffers from headaches every now and then and everybody is sick sometimes. But make sure you don’t underestimate these things! Great if it’s ‘just a headache’, but make sure you take preparatory measures and certainly don’t ignore those signs!


Are you feeling worse even though you’re staying at the same altitude? Start descending! 

To determine whether or not you’re suffering from acute altitude sickness, you can check this list: 

I have acute altitude sickness if I can say yes to all of these claims.

  1. I recently (in the last 2 days) climbed (and usually slept more than 300 meters higher than the night before).
  2. I have been at a new altitude for at least a few hours.
  3. I have a headache that wasn’t there before ascending. 


Other than that, I also suffer from at least one of these complaints: 

  1. I feel nauseous, have a lack of appetite, or have to vomit.
  2. I am very tired and feel abnormally weak.
  3. I feel lightheaded or dizzy.
  4. I have trouble sleeping, while I sleep well normally.


Do you get the same complaints during the descent? Then this is not altitude sickness, it’s impossible to get it during the descent. 


Monitor your own health: know what to do!

Do you suffer from altitude sickness? These are serious signs of your body that you should not take lightly. If you act directly, there is probably nothing wrong and after one or two days of rest you can continue your journey and enjoy it again:


  • Do not continue climbing. When you’re only suffering from the mildest version of altitude sickness, you could continue your climb of max 300 meters a day. But only when you’re just suffering from a headache that reacts to painkillers or when you’re a little bit nauseous or a little lightheaded. Don’t do this when, for whatever reason, it isn’t possible to descent again. To keep track of how the complaints develop, you can use this list. Do the symptoms continue to increase? Then descent to the point where you were still free of complaints and stay there for one or two days until you feel better. Then you can slowly go up again. If there’s no change in symptoms, try a little more rest. If the complaints continue to increase despite the rest, it is best to go down another 500 meters and find a doctor if possible.

  • Drink until you’re not thirsty anymore and your urine is light. If you’re at 4,000 meters, you’ll have to drink around five liters of water a day. Your fluid balance is disturbed and needs to come back into balance as quickly as possible.
  • There is also medication that helps against (the symptoms of) altitude sickness. Only take this in consultation with your doctor.


Chances are that you’re accompanied by a professional guide when hiking at high altitudes. It’s really important you always tell him or her how you’re feeling. The consequences of continuing when you’re suffering from the early stages of altitude sickness can be severe or even really intense. 

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Pictures: By Mountain People


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